In gas and oil wells, it is sometimes necessary to shear a tubular member disposed therein and seal the wellbore to prevent an explosion or other mishap from subsurface pressures. Typically, the oil field equipment performing such a function is known as a “blowout preventer.” One example, incorporated by reference herein, is U.S. Pat. No. 3,946,806 to Meynier. In FIGS. 1 and 2, a preventer 10 has a body 11 with a longitudinal bore 12 through which a drill pipe 15 can extend. A pair of rams 13A, 13B, extending laterally from opposite sides of the bore, are able to move axially within guideways 14 and lateral to the bore. A pair of operators 16 connected to the body at the outer ends of the rams cause the rams to move laterally and shear the drill pipe disposed therebetween with shear blades 19A, 19B. The ram shear blades are at slightly different elevations so that shear blade 19A passes slightly below shear blade 19B to effect the shearing action.
Because pressure inside the drill pipe is released upon shearing, various seals surround the rams. Seals 29A/B seal on the top of the rams that is downstream of the subsurface pressure from the ram body, side seals 25A/B, 26A/B seal on the sides of the rams, seals 37A/B seals at the rear of the blades 19A/B, and seal member 42 seals between adjacent surfaces of the blades after the shearing action. This original design effected a large change in the industry to shear using V-shaped blades. The V-shaped blades reduce an initial force required to shear the drill pipe by shearing an outer periphery first and then progressing through the remaining cross section of the pipe. However, this design proved insufficient due to leakage around the seals and particular around the seal member 42 between the adjacent blade surfaces. The seal member 42 was fitted to a fixed width slot 43 in the ram that did not axially compress the seal member 42 when the blades passed each other.
Small, but important improvements thereafter characterized the industry. A few years later, an apparent improvement over the Meynier sealing problem was disclosed in U.S. Pat. No. 4,132,265 to Williams and U.S. Pat. No. 4,132,266 to Randall. Williams and Randall teach a ram with only one V-shear blade projecting toward an opposing ram with a rectangular-face shear blade. For example, in Randall, a face seal 40 is mounted in a recess in the ram 24 so that the rectangular-face shear blade 38 after the shearing can compress in an axially direction the face seal 40. Due to other assembly issues, the face seal 40 is designed to be inserted from the side into position in a similarly shaped groove formed in the ram 24 (not shown, but used in commercial practice) to hold the face seal in position. The face seal could be compressed into a positive sealing position against the rear surfaces of the recess. The improvement converted the inadequate sliding contact of the seal member 42 of Maynier to an axially compressive sealing contact between the flat-face shear blade 38 with the flat-face seal 40. The improved contact was caused by the shear blade 38 axially compressing the face seal through contact with the blade end. Williams and Randall were able to seal higher pressures with the new design. However, Williams and Randall did not teach sealing with the V-shaped blade for the sealing contact because of the manner in which the face seal is installed from a side of the ram into position. While providing an improved seal, Williams' and Randall's design tradeoff was to abandon the V-shaped blade, resulting in an increased shearing force from using the flat-face blade instead of a V-shaped blade.
Subsequent developments moved the industry back to the double V-shaped blades with rams, but remained problematic. The flat-face blade and seal of Williams and Randall was replaced by a V-shaped blade and seal to improve the cutting of the tube. A flat rear portion of the seal was used to fit into a corresponding slot in the ram, but the seal also included a front V-shaped extension that was engageable by the V-shaped blade. The design allowed the desirable axial compression of the seal by the V-shaped blade, but led to a different problem. The additional surface area of the V-shaped seal at a given pressure with the flat base created additional forces on the blowout preventer bodies and consequent failures. The design could only be safely inserted into certain sizes of standard blowout preventers. For example, if a standard blowout preventer product line included ten standard sizes for drill pipe, only perhaps two sizes of the standard configurations were capable of the increased stress levels. While redesigned blowout preventers bodies could be made for the additional stress, the industry was adverse to new designs. Commercially, it was unacceptable to create incompatible bodies that would require the replacement of the thousands and thousands of existing bodies to use the design. For the other sizes that were unable to use the seals causing higher stresses, a variation was created that accommodated a V-shaped blade, but did not axially compress the seal. The stresses were accommodated, but the sealing was relegated to the prior art sealing designs that had proven less than desirable for the well pressures. Thus, the options were limited to either the very few sizes that could accommodate the additional stress or the less than desirable sealing by the absence of axial compression of the blade seal.
These two options have dominated the industry for approximately two decades. Despite the great needs and recognized focus, no design has produced a satisfactory solution that could combine the V-shaped blade with axial compression throughout most, if not all, of the standard blowout preventer bodies.
Therefore, there remains a need for improved sealing in a blowout preventer and similar equipment that shear and seal a tubular good used in a wellbore.